The answer to this puzzle is:
WINSTON CHURCHILL, who was Prime Minister of the UK not once, but twice (as per the title) - from 1940-45 and 1951-55.
We get this by combining the answers to each of the 3 sub-puzzles...
1. The array of numbers, headed 'pattern':
This grid conceals the sequence of prime numbers from 2 to 59, snaking a path across the rectangle in the shape of the letter 'M':

In other words, we have a PRIME M - words suggestive of 'Prime Minister'.
2. The rebus involving four jacks:
The black rectangle suggests the shape of a national flag, the two spaces in parentheses suggest the corresponding country name has 2 words, and the image below shows the set of all four Jacks in a deck of cards, i.e. the union of all the Jacks. So we need a two-word country whose flag is the Union Jack? That would be the United Kingdom...
3. The 'nth' boxes:
It is suggested that we look for 14 digits that can be split into groups of sizes (3)(2)(3)(3)(3) that appear in a row of the initial 'pattern' grid among digits that were not used in the original prime number pattern. The only row containing 14 unused digits is the top one:

If we split '23367197257173' according to the enumerations in parentheses, we get: (233)(67)(197)(257)(173). Notably, each of these numbers is a prime number. The use of 'nth' throughout this step suggests we should see 'what number prime' each is, as in what position does it occupy in the sequence of all primes. These are, respectively, the 51st, 19th, 45th, 55th and 40th prime numbers.
If we match up these to the five ordered colours above we then get: green=51, red=19, yellow=45, blue=55, and orange=40. But what to do next?
Well, how about reordering them by rainbow order: red=19, orange=40, yellow=45, green=51, blue=55. Now, we have something suspicious - a single 19 (often appearing as the first two digits in important years in recent history), and four numbers in a fairly small range, in ascending order. Couple this with the fact that the two rows of 'nth' boxes separated by dashes look like they might be runs of years, let's colour the boxes like this:

If we substitute the numbers back in, we get two year ranges: 1940-1945 and 1951-1955.
Putting this all together...
We have 3 clues that clearly point towards the identity of one particular man... Prime Minister, United Kingdom, and 1940-45 & 1951-55... Who else could this be than Winston Churchill?!
1123, correspond to the date when this puzzle was posted,11-23, which is one or more holidays. $\endgroup$